U.S. patent application number 15/803200 was filed with the patent office on 2018-03-08 for system and method of reducing corrosion in ballast tanks.
The applicant listed for this patent is Mo Husain, Gary Shilling. Invention is credited to Mo Husain, Gary Shilling.
Application Number | 20180065724 15/803200 |
Document ID | / |
Family ID | 61282332 |
Filed Date | 2018-03-08 |
United States Patent
Application |
20180065724 |
Kind Code |
A1 |
Husain; Mo ; et al. |
March 8, 2018 |
SYSTEM AND METHOD OF REDUCING CORROSION IN BALLAST TANKS
Abstract
A system and method of reducing corrosion in the ballast tanks
of a ship is comprised of a central inert gas manifold extending
down into the furthest reaches of the ballast tank, a plurality of
lateral gas distribution manifolds extending away from the central
manifold, and a plurality of downwardly projecting diffusers
connected to the lateral gas distributors that release the inert
gas at multiple simultaneous points within the ballast tank space.
A method is further presented for using the diffuser array to
sparge the ballast water with the inert gas to inhibit
microbiological induced corrosion.
Inventors: |
Husain; Mo; (Encinitas,
CA) ; Shilling; Gary; (Encinitas, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Husain; Mo
Shilling; Gary |
Encinitas
Encinitas |
CA
CA |
US
US |
|
|
Family ID: |
61282332 |
Appl. No.: |
15/803200 |
Filed: |
November 3, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
13815357 |
Feb 25, 2013 |
|
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|
15803200 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C02F 2303/04 20130101;
B63B 25/08 20130101; C02F 1/66 20130101; B63B 59/00 20130101; C02F
2209/225 20130101; C02F 2209/38 20130101; B63J 2/08 20130101; C02F
1/763 20130101; C02F 2303/08 20130101; C02F 1/008 20130101; B63J
4/002 20130101 |
International
Class: |
B63J 4/00 20060101
B63J004/00; C02F 1/66 20060101 C02F001/66; C02F 1/76 20060101
C02F001/76; C02F 1/00 20060101 C02F001/00 |
Claims
1. A method of purging for retarding corrosion in the interior of
steel ballast tanks of a double hull tanker, the method comprising:
starting an initial flow of a compressed inert gas into the bottom
ballast tank through a plurality of evenly distributed diffuser
nozzles discharging downward onto the floor of the bottom ballast
tank before the ballast water is fully pumped out of the ballast
tank; progressively increasing the flow of inert gas into the side
walls of the ballast tank through a plurality of evenly distributed
diffuser nozzles discharging downward; measuring the oxygen content
of the venting gases escaping the ballast tank; ceasing flow of the
inert gas when the oxygen content of the venting gases
substantially equals the oxygen concentration of the inert gas.
2. The method of claim 1 wherein the inert gas is composed of
approximately 84% N.sub.2, 12-14% CO.sub.2 and 2-4% O.sub.2.
3. The method of claim 1 wherein a small flow of the inert gas is
maintained through the array of diffusers during voyages of the
ship to provide a draft pressure inside the ballast tank to
preclude the influx of air;
4. The method of claim 1 wherein the compressed inert gas is cooled
to near ambient conditions prior to entering the array of diffusers
inside the ballast tank.
5. A method of reducing biological activity in a ship's ballast
water comprising sparging a gas containing elevated levels of
CO.sub.2 into a ship's ballast water through a plurality of evenly
distributed diffuser nozzles inside the ballast water hold tank
until the level of dissolved CO.sub.2 within the ballast water
reaches hypercapnia conditions that are intolerable to marine
organisms.
6. The method of claim 5 wherein the sparging gas flow is
maintained until the level of dissolved O.sub.2 within the ballast
water reaches hypoxia conditions that are intolerable to marine
organisms.
7. The method of claim 5 wherein the sparging gas flow is
maintained until the dissolved CO.sub.2 content lowers the pH of
the ballast water to conditions that are intolerable to marine
organisms.
8. The method of claim 5 wherein the sparging gas is composed of
approximately 84% N.sub.2, 12-14% CO.sub.2 and 2-4% O.sub.2.
9. The method of claim 5 wherein the biological activity within the
ballast water is further reduced by mixing a stream of ClO.sub.2
into the sparging gas until the chlorine level in the ballast water
reaches levels intolerable to marine organisms.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation-in-part of application
Ser. No. 13/815,357, filed Feb. 25, 2013, entitled "EFFICIENTLY
EFFECTIVELY INSERTING INERT GASES INTO THE ENTIRE VOLUMES AND
ULLAGE SPACES OF SHIPS' STEEL BALLAST TANKS TO RETARD INTERIOR
CORROSION" which is incorporated in its entirety herein.
FIELD OF INVENTION
[0002] The present invention generally relates to the field of
mitigation measures for saltwater corrosion of steel hulls of
tanker ships. More specifically, the present invention relates to
reducing corrosion rates of metal ballast tanks installed in
double-hulled, ocean-going ships. Large tanker ships, such as crude
oil transporters, are constructed with a plurality of compartments
or ballast tanks between the inner and outer hulls. During loading
and unloading of cargo, seawater is pumped into and out of these
ballast tanks to control the ship's buoyancy. The intermittent flow
of seawater and air into and out of these ballast tanks makes the
steel they are constructed from particularly susceptible to
oxygen-promoted corrosion and biological attack.
BACKGROUND OF THE INVENTION
[0003] Methods of preventing or mitigating oxygen-related and
biological corrosion of a ship's ballast tanks can be grouped into
three basic categories: 1) steel surface coatings, 2) cathodic
protection, and 3) air and seawater treatment. Methods of treating
the surface of the steel have involved galvanizing, epoxy coatings,
and internal liners. However generally, surface coatings do not
maintain their integrity over long periods of time and re-applying
the coating is often economically infeasible, especially for
ballast tanks which may not be readily assessible. The inherent
difficulty of inspecting and repairing surface coatings, over such
a large area of steel that is often hidden by the ship's internal
structure, makes any coating system an unreliable long-term
solution to the corrosion problem. Furthermore, ship fabricators
often prefer less effective surface coatings merely because they
are thinner and easier to apply as opposed to more effective
thicker coatings that might require more labor hours to properly
apply, adhere and cure. Studies have also shown that biological
activity significantly affects the physical properties of virtually
all surface coatings. Micro-cracks and small holes caused by acidic
bacteria are commonly found in ballast tanks. Bacterial degradation
of surface coatings has been shown to occur in ballast tanks in as
soon as 40 days after exposure to seawater microorganisms.
[0004] To further stave off corrosion of steel that is exposed to
briny seawater after the surface coating fails, ship-owners often
install a cathodic protection system. Cathodic protection systems
involve installing a sacrificial anode that is electrically
connected to the ship steel. The primary corrosion process
fundamentally involves an electrochemical reaction between iron and
other metallic constituents of the steel and dissolved oxygen.
Where seawater and metal come into contact, oxygen dissolved into
the briny seawater, gives up electrons that are readily absorbed by
the conductive metals that make up the steel. The surface metal
atoms that absorb these electrons become solubilized in the brine
and react with the ionized oxygen to form an insoluble metal oxide
that redeposits back onto the surface of the steel. Another pathway
for electrochemical corrosion involves reactions between two
dissimilar metal atoms within the steel that are connected through
a conductive solution, such as briny seawater. Thirdly,
microorganisms within the seawater that adhere to the surfaces of
the steel can excrete compounds that also promote and even
accelerate electrochemical reactions with the metal atoms of the
steel. The sacrificial anode used in a cathodic protection system
absorbs electrons donated to the steel and thereby prevents the
metal atoms on the surface from solubilizing into the brine and
redepositing. Gradually, the sacrificial anode corrodes away and
must be periodically replaced. If the anode is not replaced or the
electrical connection to the ship's steel is compromised, the
cathodic protection system is rendered useless and the accelerated
corrosion of the ship's steel quickly resumes. To be an effective
anti-corrosion strategy, cathodic protection systems involve
special installation, inspection and maintenance procedures. All
too often, however, human error and improper care typically render
cathodic protections systems an unreliable long-term solution to
the corrosion problem.
[0005] The third category of anti-corrosion strategies employed by
ship owners involves treating the seawater and/or air to reduce the
amount of free oxygen exposed to the steel. In one method, the
ballast water is pumped into on-shore storage tanks as the ship
takes on cargo. As the ship unloads cargo, the stored water is
pumped back into the ship's ballasts, thereby eliminating the need
for using fresh seawater. This recycled ballast water can be
economically treated to remove oxygen and kill microorganisms.
Having to treat fresh seawater each time it is introduced into the
ballasts would be uneconomical and might be hazardous to the
environment if the chemically-treated ballast water or leaked cargo
were discharged into local port waters when the ship is loaded.
However, not all ports-of-call have an on-shore ballast water
storage and pumping system and the ship owner often has no option
but to use fresh seawater.
[0006] The most common method of treating the air that flows into
the ballast tanks when water is pumped out is to purge the space
with an inert gas. The inert gases typically employed are "Trimix
Gas" from a generator placed aboard the ship. Trimix gas generators
intake atmospheric air and produce a gas containing approximately
84% N.sub.2, 12-14% CO.sub.2 with the balance comprising O.sub.2
and Ar (2-4%) by volume. In some older tankers, the inert gas is
drawn and scrubbed from the ship's engine exhaust, which is similar
to Trimix gas but with a slightly higher O.sub.2 content of around
5% by volume. Inert gas generators are frequently installed on
ships since International shipping regulations require the use of
an inert gas pad inside the cargo hold when transporting flammable
or hazardous substances. Most newer tanker ships use onboard Trimix
gas generators as opposed to engine flue gas.
[0007] Once the purging system gas design is selected, the next
most significant problem involves distributing the inert gas
throughout the interior voids of the ballast tanks. A
poorly-designed gas distribution system can allow residual pockets
of air to remain in relatively stagnant sections of the ballast
tank and render the corrosion mitigation effort less effective.
Since a typical ship's ballast system design employs different
sized ballast compartments spread throughout the ship's hull,
ensuring even distribution of the inert gas inside every ballast
tank presents a significant challenge to the ship's builders and
operating crew. The present invention relates to an improved method
for insuring total distribution of the inert gas within the myriad
of ballast compartments and when employed with other anti-corrosion
strategies, can greatly extend the useful life of a tanker
ship.
[0008] Previous methods of distributing the inert gas within the
ballast tanks during pump out of the ballast water have proven to
be largely inadequate because they slow down the maximum rate that
water can be pumped out. This effectively slows down the maximum
rate at which the ship can take on cargo and extends the time
required to fill the interior hull. Furthermore, some previous
methods are less preferred because they are difficult to use and
require significant maintenance expense. Still, other methods are
less preferred because they require generating more inert gas than
is needed simply to fill the ballast tank volume. Due to the
expense incurred in producing the inert gas, venting excess inert
gas into the atmosphere to reach the desired level of deoxygenation
within the ballast tanks is a significant economic deterrent. The
present invention relates to an improved method of distributing the
inert gas within the ballast system while eliminating or minimizing
the amount of leakage of inert gas to the environment. The present
invention allows the user to reach the desired level of
deoxygenation within the ballast tank atmosphere with the least
amount of inert gas being used or wasted.
[0009] Some existing inert gas distribution methods within the
ballast system are too simple to be effective at purging air out of
the ballast tanks. In one method, a single pipe discharges inert
gas at one point in the bottom of the ballast tank while a second
pipe at the highpoint of the ballast tank vents the air being
displaced. Computer modeling of this design has shown that up to
2.5 times as much excess inert gas must be moved through the
ballast tank to reduce the oxygen content to the desired level. The
cost of generating and venting this excess inert gas in addition to
the extra time required to prepare the ship for voyage represent a
significant economic detriment to the operator. One study found
that the operating costs to the shipper of pre-voyage time delays
for a large oil tanker can reach as high as $100,000 per year per
tanker.
[0010] What is needed in the art is a more efficient method of
distributing the inert gas into the complex myriad of ballast tanks
located throughout a typical tanker ship in the shortest amount of
time so that the ship can be protected from corrosion. What is
further needed in the art is a ballast tank purging system that
utilizes the least amount of inert gas to reach the desired level
of deoxygenation within the ballast tank system. What is still
further needed in the art is an inert gas delivery system that is
not so complicated or maintenance intensive as to deter its use by
the ship's crew (which leads to premature failure of ship's hull to
corrosion). What is still further needed in the art is an inert gas
distribution system that is not subject plugging from sediments
that may enter the ballast tanks and settle toward the bottom of
the tanks.
[0011] In ships fitted with a ballast control system, water is
pumped into the ballast tanks when cargo is unloaded and pumped out
of the system when cargo is loaded. In many ports-of-call, ballast
water is stored in on-shore tanks to minimize the use of fresh
seawater during these ballast cycles. Fresh seawater typically
contains any number of biological agents capable of accelerating
corrosion within the ballast tank system. Fresh seawater also
contains higher levels of dissolved oxygen, which can also
accelerate corrosion. Recycling the ballast water has a number of
beneficial purposes. First, if any material from the cargo hold
leaks into the ballast water system, that material can be collected
and separated on-shore as opposed to being discharged into the
local port waters. Secondly, the ballast water can be pre-treated
to greatly reduce its corrosive potential when pumped back into a
ship's ballast tanks. Ballast water pre-treatment using typical
chemical agents, such as oxygen scavengers and chloramines for
biological control, can add significant cost to any ballast water
recycling system, which cost is ultimately born by the shipper.
Moreover, if a port-of-call does not have an on-shore ballast water
recycling system and the shipper must discharge the ballast water
into the local port waters, potentially invasive biological species
within the ballast water pose a significant threat to the local
marine ecology as well as environmental harm from discharging
treated water. What is needed in the art is a system onboard the
ship that can treat the ballast tank water in-situ to reduce its
corrosivity potential and biological activity. In particular, where
a ship utilizes engine intering gas recycling as its ballast tank
inerting system, what is needed is a system whereby the inherent
chemistry of the inerting gas can be used to both deoxygenate and
acidify the ballast tank water during pumping. Such a system would
reduce and retard oxygen and biological-related corrosion
mechanisms within the ballast water, lower the cost of on-shore
ballast water treatment, and mitigate the risk of discharging
potentially invasive species to the local port waters.
[0012] Currently, only four methods have been approved by U.S.
Coast Guard authorities for the treatment of ballast water prior to
being discharged into local port waters. These systems largely
involve known technologies, such as filtration, UV light
sterilization, chemical treatment additives, and
electro-chlorination or electrolysis. Other methods involving
cavitation, thermal treatment and ultrasound are being promoted.
One drawback to UV light sterilization is that certain bacteria are
known to recover and survive after being exposed to it. For
example, some bacteria have been demonstrated the ability to
self-repair DNA that is damaged by UV light exposure. Another
drawback to UV sterilization is that the ballast water must be
substantially clarified prior to exposure to ensure the light
penetrates it thoroughly. Another drawback to UV sterilization is
that it is generally ineffective against animals, plants, eggs.
Onboard chemical and electrolysis systems present additional safety
concerns to ship operators. What is needed in the art is a method
of treating discharged ballast water that ensures effective
destruction of all biological agents without adding significant
cost and health and safety issues to the ship operator.
[0013] For ships with onboard inert gas generation systems to purge
the ballast tanks, the inert gas must be compressed prior to being
injected into the ballast system after ballast water pump-out
cycles. However, adiabatic gas compression can add over 200.degree.
F. to the flue gas temperature exiting the scrubbing system. Hot
inerting gas is generally less effective at purging the ballast
tanks of cold air pockets due mostly to the density difference
between the two gases. Consequently, operators would have to push
or flow more hot flue gas through the ballast tanks to achieve the
desired level of deoxygenation. Also, higher compression ratios
that might increase inerting gas flow rates to the ballast tanks
are undercut by the resulting higher flue gas temperature and
density difference compared to the cooler air pockets within the
tank. What is needed in the art is a flue gas compression and
distribution system that also includes cooling the flue gas after
compression to move more inerting gas into the tanks and make the
flue more effective at deoxygenating the ballast tanks.
DESCRIPTION OF FIGURES
[0014] FIG. 1--A plan view of a tanker ship is shown with a typical
cargo and ballast inerting system of the prior art with the
equipment and piping modifications of the current invention in
bold.
[0015] FIG. 2--A schematic of one embodiment of the current
invention as adapted to the ballast tank purging system shown in
FIG. 1 and including a heat exchanger for cooling the inert gas
after compression.
[0016] FIG. 3--A cross-sectional view of a typical tanker ship
showing on one side the complexity of the ballast compartments and
structures between the inner and outer ship hulls and a second side
showing an inert gas distribution header of the current invention
extending down into the bottom ballast tank area.
[0017] FIG. 4--A three-dimensional view of one section of a typical
tanker ship hull having the inner tank hull removed and showing
inert gas distribution manifold and the plurality of gas diffusers
projecting into the plurality of ballast compartments.
[0018] FIG. 5--A cross-section view of a typical inert gas
injection header with a downward projecting diffuser positions and
secured inside a typical bottom ballast tank of a ship.
[0019] FIG. 6--A three-dimensional view of a diffuser incorporated
in one embodiment of the current invention.
[0020] FIG. 7--A schematic of one embodiment of the current
invention where a ship's existing inerting gas supply system is
modified to incorporate features of the current invention.
SUMMARY OF THE INVENTION
[0021] The present invention presents an improved system for
deoxygenating the gases within a ship's ballast tank system by
increasing the number of locations within the ballast tank system
where the inerting gas is injected. Instead of a single or dual
point of injecting the inerting gas into the complex
compartmentalization of the ballast system, the ballast tank is
fitted with an inert gas distribution manifold throughout to
ballast tank system to more uniformly distribute the inert gas into
the various compartments of the tank, to speed up the time required
and use the least amount of inert gas to reach the desired level of
deoxygenation that protects the ship's steel hull from
corrosion.
[0022] The present invention also presents the use of gas diffusers
at each point where the inert gas is injected within the
distributed ballast gas manifold. When the ballast system is
flooded and being pumped out, the inert gas exiting the diffusers
helps stir and suspend any sediments that may have settled within
the ballast tanks, allowing their removal with the outflowing
ballast water. When the ballast system is dry, diffusers greatly
increase mixing of the inert gas with any air that may have been
drawn into the pump-out of the ballast water. The use of diffusers
for distributing the inert gas within the ballast tank system
further reduces the time required and requires less inert gas to
reach the desired level of deoxygenation to protect the ship's
steel hull from corrosion. In one embodiment, the compressed inert
gas is first cooled before being injected into the ballast tanks.
The cooler inert gas more easily mixes with any air drawn into the
ballast system during pump-out of the ballast water, which also
further speeds the time required to reach the desired level of
deoxygenation and reduces the amount of inert gas being wasted by
venting.
[0023] The present invention also presents the use of a distributed
network of gas diffusers throughout the ballast system to allow the
direct sparging of the ballast water. By sparging the ballast water
with an inert gas, CO.sub.2 can dissolve into and slightly acidify
the ballast water to aid in killing microbiological activity.
Moreover, the inert gas sparging of the ballast water aids in
stripping dissolved oxygen within the water, which provides further
reduction in corrosivity of the ballast water to the ship's steel
hulls. The invention further presents a method and device for
adapting the ship's inerting gas system to sparging shore-based
ballast storage tanks and floating side-barge tanks for controlling
microbiological activity within those vessels prior to the ballast
water being pumped back into the ship's ballast system.
[0024] The present invention also presents a system for
retrofitting an existing ship's inert gas generation system to
accommodate the features of the invention.
DETAILED DESCRIPTION
[0025] In reference to FIG. 1, a plan view of a typical liquid
tanker ship is shown. The inert gas generating system is located
below the top deck where an existing distribution manifold 1
extends through a deck seal arrangement 2. A plurality of valves 3
allow operators to deliver the compressed inert gas in the
distribution manifold into the cargo holds and into the ballast
tanks. Each ballast compartment is fitted with a pressure/vacuum
relief valve to protect the compartment's integrity and prevent
over/under-pressurization. A new isolation valve 5 is installed and
new piping routes the compressed inerting gas over to a heat
exchanger 6. The compressed inerting gas can be cooled using air or
water pumped from a suitable source. The compressed gas exiting the
heat exchanger reconnects to the primary distribution manifold. New
branch connections 7 direct the cooled, compressed inerting gas
into a plurality of distribution tubes 8 that extend down into the
bottom of each ballast tank.
[0026] In reference to FIG. 2, a schematic is shown of a modified
inert gas booster compression system of the current invention.
Inerting gas a ship's existing nitrogen generator flows through an
isolation valve 20. A pair of redundant compressors 22 are
connected in parallel where typically only one compressor is
operated while the other is isolated and idle. Compressed hot
inerting gas next flows through additional piping and into a heat
exchanger 23. In the embodiment of FIG. 2, the source of cooling is
fresh seawater that is strained, pumped and filtered. The warmed
seawater then is discharged back into the local waters. In another
embodiment, the source of cooling is air circulated by fans across
finned tubes carrying the compressed inerting gas. The cooled
inerting gas then flows into the ship's existing Inert Gas Supply
(I.G.S.) distribution system.
[0027] In reference to FIG. 3, a cross sectional view of a typical
midship ballast tank is shown. The topside ballast tank 30, a
hopper tank 31 and a double-bottom tank 32 are all in communication
to form a continuous ballast tank system bordering either side of
the main cargo hold tanks 33. During the ship's construction,
various steel members are welded to the outer side of the cargo
hull to reinforce the inner hull. This cargo hull reinforcing steel
projects raised surfaces into the ballast tank space, which creates
a complex array of interconnected compartments within the ballast
tank system. The complex geometry of the ballast tank space further
exacerbates the inerting process by inhibiting the free-flow
pathway of the purge gas. In one embodiment of the current
invention, a common inert gas downpipe 40 is connected to the main
I.G.S. distribution manifold. One or more ballast purge vents 41
ports extend above the ballast tanks where air or inert gas can be
vented when ballast water is being pumped into the tanks. When
ballast water is pumped out of the tanks, air typically is drawn
back into the ballast tanks through these vents and must be
subsequently purged out of the ballast tank with the inerting gas.
Excess inert gas that flows into the ballast tank is vented back
out. These vent ports provide a relatively easy point to measure
the oxygen content. Once the oxygen level of the vented gas reaches
the desired level, the operator can shut off the inerting gas valve
and cease flow. In one embodiment of the current invention, the
inerting gas flow rate into the ballast tank equals or is slightly
higher than the rate water is pumped out such that air is prevented
from re-entering the ballast tanks through the exhaust vents.
[0028] In continued reference to FIG. 3, the inert gas distribution
system inside the ballast tank is comprised to one or more vertical
pipe sections 42 with each vertical pipe section having a plurality
of lateral pipe sections 43 evenly distributed throughout the
sidewall of the ship. An angled section 44 extends from the
vertical pipe section over to a horizontal pipe section 45. The
horizontal pipe section also has a plurality of laterals 46 evenly
distributed throughout the channels of the double-bottom ballast
tanks. Projecting downward from the plurality of laterals are a
plurality of diffusers 47 through which the inert gas passes into
the ballast tank space. The diffusers are pointed downward to aid
in the stirring of sediments so that they remain suspended within
the exiting ballast water and do not collect within the bottom of
the ballast tank.
[0029] In reference to FIG. 4, a 3-dimensional cross section of the
outside hull and ballast tank system of a typical double-hull
tanker ship is shown with an embodiment of the current invention
installed. A plurality of ell-shaped reinforcing bulkheads 40 are
attached to the exterior hull steel wall 41. Once the inner steel
hull is cladded to these rib sections, a plurality of ballast
compartments is formed. Holes are located at multiple points within
the bulkheads 40 so that ballast water can readily flow throughout
the plurality of ballast compartments. A typical tanker ship will
have several groups of these ballast systems connected together to
form the ship's ballast control system. Each ballast tank has a
vent header 42 that collects gases that are being purged out of
each ballast compartment. One or more vent points 43 project above
the upper deck of the ship. A distribution manifold 44 is connected
to the ship's main I.G.S. header. In one embodiment, the plurality
of laterals extends through separate holes bored into the
reinforcing ribs such that the flow distribution holes are not
impeded. Extending downward from the laterals inside each of the
ballast compartments, one or more diffusers 46 are connected to the
horizontal pipes 45 that inject the inerting gas directly into each
ballast compartment.
[0030] In reference to FIG. 5, a cross sectional view of one of the
horizontal pipes 45 extending into one of the double-hull bottom
ballast tanks is shown. The horizontal pipe is suspended above the
floor of the compartment by pipe supports 46. Extending below
horizontal pipes, a threaded diffuser nozzle 47 is in communication
with the inerting gas flowing through the horizontal pipes through
a threaded pipe nipple 48. In this embodiment, a layer of sediment
49 is shown settling atop the bottom steel hull 50. In this
orientation, the sediments are less likely to plug the diffuser's
gas discharge opening and as the inerting gas flows into the bottom
ballast tanks, stirring of the sediments is promoted. The suspended
sediments are more easily removed from the tanks with the
outflowing ballast water. Depending on the size of the ballast
tank, one or more of these downwardly projecting diffusers can be
attached to the horizontal pipes. In one embodiment, two diffusers
are installed on the horizontal pipes and evenly spaced apart
within each bottom ballast tank.
[0031] In reference to FIG. 6, a diffuser of one embodiment of the
invention is shown. The diffuser has a threaded male fitting on one
end that is fastened to a matching threaded female fitting on the
inerting gas piping. A gripping section 61 allows the use of
standard tools to secure the diffuser into the piping fitting. The
diffuser has a converging nozzle 62 that accelerates the inerting
gas toward the discharge slit 63. In this embodiment of the
invention, pressure losses in the inerting gas piping are minimized
by keeping the gas velocities relatively low. However, at the
diffuser, the gas velocity is greatly accelerated so as to provide
the greatest stirring and mixing action in the environment around
the diffuser. When the ballast tanks are flooded with water, the
accelerated inert gas stirs sediments so they can be removed with
the outflowing ballast water. When the tanks are empty of ballast
water, the accelerated inert gas exiting the diffuser greatly
improves the rate of mixing and purging of the oxygen within the
tank gases, which allows the ballast tanks to be deoxygenated to
the desired level in a much shorter time than conventional inerting
gas systems.
[0032] In reference to FIG. 7, a schematic of a ballast inerting
system of the current invention is shown being retrofitted to an
existing I.G. System (IGS) aboard a typical tanker ship having a
ballast control system. Because the diffusers greatly accelerate
the inert gas at the point of release into the ballast
compartments, the pressure loss under flowing conditions can be
quite high. In one embodiment, the required gas pressure upstream
of the diffuser is up to 60 prig. Since conventional IGS delivery
systems do not employ a distributed array of diffusers positioned
throughout the ballast tanks, the existing inert gas compressors
would not provide sufficient pressure to overcome the diffuser
pressure loss and any additional pressure losses incurred under
flowing conditions. Consequently, in the embodiment of the current
invention, new gas compressors will have to be provided to provide
the required gas pressure under flowing conditions. A typical
tanker ship IGS includes an inert gas generator or source 70. If
the inert gas is engine exhaust, the gas will pass through a gas
scrubber 71 to remove contaminants. The inert gas then passes up to
the deck of the tanker ship through a deck seal 72. The suction
piping to the new gas compressors 74 ties into the existing above
deck IGS piping at 73. The discharge piping from the new gas
compressors 74 ties into the ship's main IGS header at 75, which is
downstream of an isolation/bypass valve 76. A typical tanker ship
has a plurality of individual cargo hold tanks that are each
connected to the IGS header to deliver inerting gas to the
head-space above the cargo. In one embodiment of the current
invention, the ballast tank inerting gas connects to the cargo
inerting header upstream of the control valve at 77. A second
ballast IGS control valve 78 is provided to isolate the ballast
system from the IGS system. The valves controlling the flow of
inerting gas either to the cargo hold or the ballast system can be
fully automated with electronic or pneumatic actuation, or can be
manually actuated, or some combination of the two depending on the
level of automation desired by the ship owner/operator.
[0033] The present invention particularly concerns progressively
and sequentially blowing a relatively cool inerting gas through
diffusers, having sufficient flowing gas pressure drop to remedy
any clogging by sediments, into the entire volume of a double hull
tanker's ballast tanks to retard corrosion in the interior of the
ballast tanks. Furthermore, the diffusers in the bottom ballast
tanks inject the inerting gas downward onto the floor of the hull
to stir up sediments so they can be removed from the ballast tanks
during periodic pump-out of the ballast water. Furthermore, the
present invention concerns sparging the ballast water stored in the
ballast tanks, on-shore tanks, or side-floating tanks through an
array of diffusers with an inerting gas to `kill` aquatic nuisance
species.
[0034] By extending the points of inert gas injection also into the
side walls of the ballast tank, fewer air pockets will remain in
the upper ballast tanks, where often the worst corrosion occurs
compared to prior art systems. By installing a plurality of
symmetrically arranged inert gas injection points within the
ballast tank, greater operational flexibility can be achieved. In
one embodiment, a low flow of inert gas is injected for a short
period of time to allow a more subtle air purging rate that better
renders difficult-to-reach spaces at least partially deoxygenated
while using a lesser amount of inert gas. After this initial
injection period, the inert gas flow may be accelerated in steps
over time until the vented gas reaches the desired level of
deoxygenation. By using diffusers at each point of injection, as
the flow rate of inert gas increases, better distribution of the
inert gas within the ballast tank space is achieved. Because using
diffusers increases the pressure drop of the inert gas being
injected into the ballast tank, higher output pressure compressors
will need to be employed for use with the current invention. Since
higher compression ratios result in excessive heating of the
inerting gas, cooling the gas prior to entering the ballast tank
brings the inerting gas' density closer to that of the air it will
be displacing and mixing efficiency is greatly improved. During
sparging of the ballast water, the cooler inerting gas also creates
better bubble distribution at the outlet of the diffusers. By
increasing the pressure of the inert gas, diffusers with smaller
outlet slits can be used, which are less likely to allow ingress of
sediments that could plug the diffuser and are more effective at
creating sparging bubbles when gas is injected into the ballast
water for deoxygenation and microbial corrosion mitigation. When
sparging the ballast water, a higher inerting gas pressure is also
required to overcome the static head of the ballast water within
the tank. For inert gas compressors requiring 20 psi for the
diffuser pressure drop and up to 40 psi for the static head of the
ballast water, compressor discharge pressures of up to 60 prig are
required. At this compression ratio, the inerting gas could leave
the compressor at over 130.degree. F., which would greatly benefit
from cooling prior to injection into the ballast tank during
deoxygenation of the ballast air space. Since many existing ship,
barge or on-shore inert gas generators cannot generate the outlet
pressures required for adequate flow through the diffuser array of
the current invention, gas booster compressors may be required to
be installed downstream of the inerting gas generator.
[0035] The present system uses inert gas to sparge the ballast
water (i) to retard interior corrosion in ballast tanks of a double
hulled tanker (ii) to "kill" harmful aquatic nuisance species in
ballast water of double hulled tanker, and (iii) killing of
organisms in shore based tanks or in shore-side floating tanks. The
diffuser array for the ship ballast tanks, onshore tanks, or
side-floating tanks are symmetrically distributed near the bottom
of the tanks. The diffuser array is also symmetrically distributed
throughout the side walls of the ship's ballast tanks. The number
of diffusers and their location within the tanks are based on each
tank's particular design layout.
[0036] A computer system controls the inert gas feed valves at each
different level within the tank according to (1) the relative gas
density and temperature differences between the inert gas being
introduced into a tank and the ambient gas or air currently in the
tank, (2) the rate of inert gas flow relative to tank capacity (at
each successive level), and (3) a time sequence by which the lower
regions of the tank are progressively first inerted, pushing the
air upwards and out through vents at the top of the tank. During
air purging cycles, as the level of deoxygenation progresses within
the ballast tank, the control system can adjusts the flow of
inerting gas at each level of the horizontal laterals branching off
of the central injection header to minimize the amount of inerting
gas needed and shortening the amount of time required to achieve
the desired oxygen levels.
[0037] Using the same array of inert gas injection diffusers for
deoxygenating the space of the empty ballast tank, the current
invention employs in situ sparging of the ballast water within the
ballast tank to kill harmful organisms. When a low-oxygen inerting
gas is sparged into the ballast water, the ballast water becomes
deoxygenated (hypoxia) and detrimental to aerobic marine life
survival. When a high-CO.sub.2 inerting gas is sparged into the
ballast water, the ballast water's pH is acidified due to
dissolution of CO.sub.2 into the water and the formation of
carbonic acid HCO3-- (hypercapnia). Acidification of the ballast
water is detrimental to both aerobic and anaerobic marine life
survival. One objective of the current invention is to use the
commonly available marine inerting gas generators to change the
chemistry of the ballast water to destroy aquatic nuisance species
and to mitigate corrosion from other microbiological agents within
the ballast system.
[0038] In one embodiment of the invention, dissolved O.sub.2
concentrations in the ballast water were reduced to 10% saturation
and the pH was reduced to 5.5 after 10 minutes of sparging with the
Trimix inerting gas. All organisms except of Vibrio cholerae showed
no mortality in aerobic conditions. The shrimp and crabs incubated
in "trimix" were dead after 15 minutes and 75 minutes,
respectively. Even a transfer into aerated water did not result in
any movement. The brittle stars incubated under nitrogen started to
move again after transferred into aerated water. The shells of all
the mussels sparged with the Trimx inerting gas were open
(indicating mortality) after 95 minutes. Mortaility of the barnacle
species were also confirmed after 95 minute sparging with the
Trimix gas. Mortaility of plankton copepods was confirmed after
only 15 minutes of sparging with the Trimix inerting gas.
[0039] By sparging the ballast water with readily available trimix
gas found on most ships to cause hypoxia and/or hypercapnia, a
substantial variety of marine organisms will be destroyed. In most
cases where the ballast water is sea water, trimix gas will
eliminate the need for addition of biocides or other chemicals.
However, where the ballast water is fresh water, the extent of
acidification caused by the trimix gas sparging is slightly reduced
and some addition of a biocide, such as chlorine dioxide or
chloramine, may be necessary to achieve the level biological
mortality required. In one embodiment of the current invention, the
ballast water is sparged with the trimix gas until the dissolved
CO.sub.2 is at least 50 ppm. In one embodiment of the current
invention, the ballast water is sparged with the trimix gas until
the dissolved CO.sub.2 is at least 20 ppm. In one embodiment of the
current invention, the ballast water is sparged with the trimix gas
until the dissolved CO.sub.2 is at least 500 ppm The CO.sub.2 level
is increased to achieve a sufficient level of marine biological
mortality. In another embodiment, the ballast water is sparged by
the trimix gas until the level of dissolved oxygen less than
.ltoreq.0.8 ppm to achieve a sufficient level of marine biological
mortality. In another embodiment, the ballast water is sparged by
the trimix gas until the pH is lowered to at least 6.0 to achieve a
sufficient level of marine biological mortality.
[0040] In one embodiment, the device kills all aquatic nuisance
species (ANS) in the entire volume of ballast water in a shore
based tank or in shore side floating tanks, such as in a barge or
in converted ships, specifically designed to receive polluted
ballast water. Of particular concern is ballast water treatment for
ballast water temporarily contained in shore based tanks or shore
side floating tanks, such as in a barge or in a converted ship by
infusion and diffusion of inert gas into ballast water and elevated
CO2 and simultaneously adding mild chlorine without harming the
ballast water discharge. The ballast water can be diffused through
special diffusers such that ingress of sediments in the diffuser is
nearly impossible.
[0041] The following table presents the flow rates, capacity
requirements and dimensional requirements for an onshore ballast
water treatment system for 24-hour capacities ranging from about
1,000 cubic meters per day to around 15,000 cubic meters per day.
Values are expressed in a range of units to facilitate use of the
table elements.
[0042] The table presents the rates of continuous flow of water for
the processing facility, sizes of the processing structure, and
size of holding facilities needed. For example, an onshore ballast
water treatment facility for processing 10,902 cubic meters per day
requires a square processing facility with 160 feet per side. The
capacity to hold 10,902 cubic meters of water can be provided by a
round tank or comparable pond 10 feet deep with a radius of 110.7
feet.
TABLE-US-00001 DESIGN OF ON-SHORE BALLAST WATER TREATMENT FACILITY
FOR CAPACITIES FROM 1090.2 TO 14,172.6 CUBIC METERS PER DAY Rate of
Continuous Flow Water Treatment At 2 hours water treatment rate
Rate of Per Minute Gallons 200.0 800.0 1,400.0 2,000.0 2,600.0
Continuous Cubic feet 26.7 107.0 187.2 267.4 347.6 Flow of Cubic
meters 0.8 3.0 5.3 7.6 9.8 Water to Per Hour Gallons 12,000.0
48,000.0 84,000.0 120,000.0 156,000.0 Be Treated Cubic feet 1,604.3
6,417.1 11,229.9 16,042.8 20,855.6 Cubic meters 45.4 181.7 318.0
454.2 590.5 Per Day Gallons 288,000.0 1,152,000.0 2,016,000.0
2,880,000.0 3,744,000.0 Cubic feet 38,502.7 154,010.7 269,518.7
385,026.7 500,534.8 Cubic meters 1,090.2 4,360.8 7,631.4 10,902.0
14,172.6 Size of Size of Square Feet (8 foot height) 400.0 1,600.0
6,400.0 25,600.0 102,400.0 Processing Square Square Meters (2.44
meters height) 37.2 148.6 594.6 2,378.3 9,513.3 Structure
Processing Feet per side 20.0 40.0 80.0 160.0 320.0 Structure
Meters per side 6.1 12.2 24.4 48.8 97.5 Size of Size of Square Feet
(10 foot height) 3,850.3 15,401.1 26,951.9 38,502.7 50,053.5
Holding Circular Square Meters (3.05 meters height) 357.7 1,430.8
2,503.9 3,577.0 4,650.1 Facilities Holding Radius in feet 35.0 70.0
92.6 110.7 126.2 Facility Radius in meters 10.7 21.3 28.2 33.7
38.5
[0043] The above table illustrates a range of design parameters,
recognizing that the capacities described can be scaled up to
accommodate the largest of requirements. The onshore ballast water
treatment system must be custom designed for each port with the
driving design element being the maximum amount of discharged
untreated ballast water that must be a accommodated each day. This
element can be determined by considered the number of ships in
port, amount of cargo they will be loading and the amount of time
it will take to load the cargo.
[0044] Testing Methods.
[0045] Three parallel incubations were done for each experiment.
Several organisms were incubated in 1.5 L of seawater at 22.degree.
C. in large Erlenmeyer flasks. Each incubation was equilibrated
with the respective gas using aquarium stones before any organisms
were introduced. The aerobic control was bubbled from an aquarium
pump for approximately 15 min and left open to the atmosphere after
addition of specimens. An anaerobic incubation was bubbled with
99.998% nitrogen for 15 min. After introduction of the organisms,
the bubbling was continued for another 10 min and then the
container was closed with a rubber stopper or the bubbling was
continued. The incubation in trimix was treated similarly except
that the gas mix was used instead of nitrogen. The oxygen
concentrations were measured after the initial bubbling period
using a Strathkelvin oxygen electrode with a Cameron instruments
OM-200 oxygen analyser. Ph values were determined using a
combination electrode and a Radiometer pH meter.
[0046] Survival of the specimens was determined visually by
checking for motile responses to tactile stimulus (e.g. mussels do
not close their shells, barnacles to not withdraw their feet,
shrimp do not move their mouthparts, worms appear limp and
motionless). After each testing of the animals, the incubation
flasks were bubbled for 10 min to reestablish original conditions.
To verify survival of the specimens, they were relocated to aerobic
conditions and checked again after 30 min. If they still did not
respond, they were considered dead. The survival of the bacterium
Vibrio cholerae strain N16961 was monitored by repeated plating on
Luria-Bertani Agar with Rifampicin (100 .mu.g/mL). This setup
allowed us to compare responses to nitrogen and "trimix" while
making sure that test specimens were not gravely affected by other
experimental parameters. Incubation in pure nitrogen allow for a
comparison with published results by others.
[0047] The oxygen concentrations were measured at "non-detectable"
for the nitrogen incubations and 10% air saturation (=16 Torr
partial pressure) for the "trimix". The pH value of the water
bubbled with trimix reached 5.5 after the initial 10 min of
vigorous bubbling. The aerobic and nitrogen bubbled seawater
maintained their pH at 8. The incubations showed clearly that
"trimix" kills organisms considerably faster than incubations in
pure nitrogen Table 1. All organisms except of Vibrio cholerae
showed no mortality in aerobic conditions. The shrimp and crabs
incubated in "trimix" were dead after 15 min and 75 min,
respectively. Even a transfer into aerated water did not result in
any movement. The brittle stars incubated under nitrogen started to
move again after transferred into aerated water. All the mussels
incubated in nitrogen and "trimix" were open after 95 min but only
the ones in nitrogen still responded to tactile stimuli by closing
their shells. The barnacles were judged dead after incubation in
"trimix" when they did not withdraw their feet when disturbed, the
ones incubated in nitrogen still behaved normally. The plankton
sample mainly contained copepods. They stopped moving after 15 min
and could not be revived in nitrogen and "trimix" incubations. The
results are summarized below.
TABLE-US-00002 Number/ Species incubation Nitrogen Trimix Comments
Mimulus Crab 7/inc Normal Dead after foliatus 75 min Mytilus Mussel
10/inc Open but 6 dead after californianus responding 95 min
Pollicipes Barnacle 10/inc Normal Dead after polymerus 60 min
Megabalanus Barnacle 5 Dead after Dead after californicus 84 h 48 h
Sebastes Rockfish 2 Dead after Dead after diplopora 19 min 7 min
Ophionereis Brittle 5-10 Most survive Most survive Mean of 4
annulata star up to 3 h, up to 3 h, experiments most dead several
dead after 26 h after 26 h Ophioderma Brittle 8/inc Not moving but
Dead after panamanse star revivable by air 50 min Unidentified
Caridean 6 Affected but Dead after shrimp alive after 25 min 30 min
Unidentified Caridean 6 2 dead after 5 dead after shrimp 30 min 45
min Mysolopsis Mysid 25 Dead after Dead after californica shrimp 15
min 15 min Lysmata Shrimp 10/inc Normal Dead after californica 20
min Plankton Var. lots Dead Dead after mix copepods 15 min
Tigriopus Copepod 8-10 Dead after Many dead Mean of 3 californicus
2 h after 2 h experiments Vibrio Bacterium 2.5 .times. 10.sup.6/ml
>>99% dead >>99% dead Aerobic: cholerae after 24 h
after 24 h 30% dead after 24 h
[0048] Two effects have to be distinguished when looking at
"trimix" incubations in seawater: a) the lowering of the pH from pH
8 to about 5.5 and b) the raised CO.sub.2 concentrations in the
water. While the pH change caused by the incubations in "trimix"
are in the range of published experiments, the CO.sub.2
concentration in "trimix" (about 14%) is much higher than those
investigated in the published literature (0.1% to 1%). Therefore,
the effects of "trimix" incubations should be much stronger than
those published previously.
[0049] The trimix combines two effects on organisms--hypoxia and
hypercapnia. Preliminary results demonstrate the effectiveness of
this combination in quickly killing a variety of sample organisms.
Contrary to methods using additions of biocides or any chemicals in
general, nothing is added to the ballast water and, therefore,
nothing will be released into the environment when it is released
again. Methods using radiation, heating, or filtering ballast water
before or during a ship's trip, are much more expensive. The
equipment needed to establish a rapid gassing of ballast water is
available off the shelf and has been used in the marine
environment. The plumbing and gas release equipment has been
optimised and has been used in application such as aquaculture,
sewage treatment and industrial uses. Extensive supporting
literature and research about the design and optimisation of
equipment for the aeration of water is available from public
resources. Inert gas generators are available for fire prevention
purposes on ships and other structures and are already installed on
many ships, mainly tankers. They can use a variety of fuels
including marine diesel to generate the inert gas.
[0050] In order to increase the efficacy of the Trimix mentioned
above, especially regarding microorganisms, we can optionally add
an additional agent to the treatment, the gas chlorine dioxide
(CLO.sub.2). Chlorine dioxide is a compound that is widely used
since the early 1900s for a variety of commercial water treatments
including disinfections of pool water, waste water, and drinking
water (see e.g. "Chlorine Dioxide", EPA Guidance Manual, chapter 4,
EPA 815-R-99-014, 1999). The concentration of chlorine dioxide in
drinking water treatments is between 0.2 and 2 ppm, in other
applications the concentration varies depending on the degree of
contamination. It is usually added to the water to be treated as a
solution in water (typically in concentrations up to 1%) or, if
needed in large quantities, is generated on site through
commercially available generators (e.g., EVOQUA Water Technologies,
210 Sixth Ave, suite 3300, Pittsburgh, Pa. 15222, USA;
WWW.evoqua.com). The chemical reactions caused by the addition of
CLO.sub.2 to the system described earlier are:
CO.sub.2+H.sub.2O.fwdarw.H.sub.2CO.sub.3H.sup.++HCO.sub.3.sup.-
CLO.sub.2+e.sup.-.fwdarw.CLO.sub.2.sup.-
CLO.sub.2.sup.-+4H.sup.++4e.sup.-.fwdarw.Cl.sup.-+2H.sub.2O
The action of chlorine dioxide on organic materials such as those
in microorganisms depends on oxidation and, therefore, alteration
of proteins and RNA inside of cells.
[0051] The present invention contemplates the infusion of inert, or
combustion, gases into ballast water--in order to kill harmful
aquatic nuisance species by simultaneous, synergistic, inducement
of (1) hypercapnia (elevated concentration of dissolved CO.sub.2),
(2) hypoxia (depressed concentration of dissolved O.sub.2), (3)
acidic pH level and (4) chlorine dioxide. As discussed previously,
the inerting gases may be obtained, for example, from (i) a ship's
inert gas generator, or from (ii) ship's own flue gases, or from a
standard marine inert gas generator. These gases are highly
noxious, having CO.sub.2 significantly increased and O.sub.2
significantly depleted, from normal atmospheric levels. An
air-breathing animal--not only humans, but lower animals--would
soon be stifled by these gases. Thus one way to think about the
prophylactic action of present invention is to consider that the
present invention effectively and efficiently alters the mixture of
atmospheric gases, including oxygen (O.sub.2), that normally are
dissolved in ballast water in favor of, predominantly, carbon
dioxide (CO.sub.2). Aquatic marine organisms--at least of the
aerobic types--can scarcely tolerate these noxious gases any better
than can air-breathing animals, and a widespread and severe die-off
of multiple marine organisms, is experienced in the presence of
these noxious gases dissolved in sea water.
[0052] This condition of enhanced dissolved CO.sub.2 which is of an
extreme level such as strongly induces hypercapnia in marine
organisms--is, in accordance with the present invention, preferably
realized by infusion of a mixture gases into the seawater, which
gaseous mixture is preferably enhanced in CO.sub.2.gtoreq.11% by
molar volume and, more preferably, to .gtoreq.15% by molar volume.
In accordance with the invention, these gases enhanced in CO.sub.2
are preferably realized as the gaseous output of a standard
shipboard inert gas generator (commonly called a Holec generator,
or a Maritime Protection generator, after the major manufacturers
thereof) output of which is commonly about 84% Nitrogen, 12-14%
CO.sub.2 and 2% Oxygen), and/or as a ship's own flue gases. These
preferred CO.sub.2 concentrations may be compared with, by way of
example, published studies of hypercapnia in marine organisms that
have generally investigated introduction of gaseous mixtures having
CO.sub.2 concentrations in the range from 0.1% to 1%. In accordance
with the present invention, effective delivery of the gases high in
CO.sub.2 concentration into ballast water will be realized by
bubbling these gases into ballast water mostly from the diffusers
located at the bottom of the ballast water tank. However, it may be
necessary to bubble the gases from the diffusers purposely located
at the side and as well locations with dense and complex
structures; dense and complex structures are `pre-disposed` to
negate adequate diffusion of inert gas in the ballast water.
[0053] The infusion of the gases enhanced in percentage CO.sub.2 is
preferably continued until dissolved CO.sub.2 in the ballast water
is raised to .gtoreq.20 ppm, and more preferably to .gtoreq.50 ppm.
Dissolved CO.sub.2 of this level serves to acidify sea water. The
chemical mechanism by which enhanced dissolved CO.sub.2 acidifies
seawater is:
CO.sub.2+H.sub.2O..fwdarw.H.sub.2CO.sub.3HH.sup.++HCO.sub.3.sup.-
Dissolved CO.sub.2 of the preferred levels of 20 ppm reduces the pH
of seawater, which is normally 8, to acidic levels of pH 7, and,
preferably, pH 6 and still more preferably pH 5.5.
[0054] This enhancement is based on the recognition that (i)
aquatic nuisance species present in ship's ballast water may best
be controlled by a combination of hypoxic, hypercapnic and acidic
conditions within the ballast water, and that (ii) these conditions
may be simultaneously economically realized by bubbling gases from
an inert gas generator, and/or the flue gases of the ship, through
the ballast water. The preferred levels of dissolved CO.sub.2 i.e.,
preferably .gtoreq.20 ppm, and more preferably to 50 ppm), and the
preferred pH levels (i.e., to pH.ltoreq.7, and, preferably,
pH.ltoreq.6 and still more preferably pH.ltoreq.5.5), have already
been stated. In accordance with the present invention, the oxygen
content of a gaseous mixture that infused with ballast water is
preferably .ltoreq.4% O.sub.2, and is more preferably .ltoreq.3%
O.sub.2, and this infusion of is continued until a dissolved oxygen
level of, preferably, .ltoreq.1 ppm O.sub.2 and, more preferably,
.ltoreq.0.8 ppm O.sub.2 is induced.
[0055] Important to understanding the present invention, it should
be appreciated that the method of the invention is managing at
least four different conditions--each of two dissolved gases, and
acidity/alkalinity--all at the same time. To appreciate that the
conditions are separate, and separately managed, understand to
begin with that hypoxia, or lack of oxygen, implies neither
hypercapnia--an excess of carbon dioxide--nor acidity--a pH less
than seven. For example, oxygen present in ullage space gases
and/or as a dissolved gas in ballast water may be replaced with
nitrogen without appreciable effect on either (i) the dissolved
carbon dioxide within, or (ii) the pH balance of, the ballast
water.
[0056] Likewise, it should be understood that hypercapnia, or an
excess of carbon dioxide, does not mandate hypoxia, nor an acidic
pH. For example, the carbon dioxide level in the enclosed
atmosphere of a submarine can, as a product of human respiration,
rise to high levels but that it is "scrubbed" from the atmosphere.
The build-up of CO.sub.2 can transpire in an enclosed space
nonetheless that the atmosphere may constantly contain copious
oxygen (derived on a nuclear submarine from the electrolysis of
water with electricity).
[0057] Finally, even when carbon dioxide is added to water--as it
sometimes is by aquarists to promote the lush growth of aquatic
plants--this augmentation of dissolved CO.sub.2 gas need not result
in decreased pH (increased acidity) of the water (by the same
chemical mechanism as occurs in the present invention) if, as is
often the case, any lowering of the pH level is counteracted by the
addition of a chemical base such as, most commonly, lime.
[0058] One embodiment of the ballast water treatment method in
accordance with the present invention consists of (i) bubbling an
oxygen-depleted, CO.sub.2-enhanced, inert gas mixture via a row of
pipes (orifices at the bottom of the pipes) located at the bottom
of a shore based ballast water storage tank.
[0059] The inert gas is preferably from a standard Marine inert gas
generator, and is commonly composed of about 84% Nitrogen, 12-14%
CO.sub.2 and 2%-4% Oxygen. In accordance with the present
invention, the ballast water is equilibrated with gases from the
inert gas generator. As a result, the water will become hypoxia,
will contain CO.sub.2 levels much higher than normal, and the pH
will drop from the normal pH of seawater (pH 8) to approximately pH
6.
[0060] Therefore, in one of its aspects the present invention is
embodied in a method of killing aquatic nuisance species in ship's
ballast water. The base method consists simply of infusing carbon
dioxide into the ship's ballast water at a level effective to kill
aquatic nuisance species by hypercapnia, with effectivity of
killing harmful organisms is enhanced by adding chlorine dioxide.
The infusing is preferably with a gaseous mixture of 11% carbon
dioxide by molar volume. This infusing with the gaseous mixture of
11% carbon dioxide preferably transpires until the ballast water is
hypercapnic to 5 ppm dissolved carbon dioxide. This infusing
preferably transpires by bubbling the gaseous mixture through the
ballast water. The base method is preferably expanded, or enlarged,
to include concurrently depleting oxygen in the ship's ballast
water at a level effective to kill aquatic nuisance species by
hypoxia.
[0061] In this expanded method the infusing is preferably like as
in the base method, with the depleting preferably transpiring by
substitution of gases, including oxygen gas dissolved in the
ballast water, with a gaseous mixture of 4% oxygen. This depicting
with a gaseous mixture of 4% oxygen preferably transpires until the
ballast water is hypoxic to 1% ppm dissolved oxygen.
[0062] In either the base, or the expanded, method, the infusing
and/or the depleting may be, and preferably is, accompanied by
acidifying of the ship's ballast water at a level effective to kill
aquatic nuisance species by enhancing with Chlorine Dioxide. This
acidifying is a consequence of the infusing where, as is preferred,
the infusing is with a gaseous mixture of 11% carbon dioxide by
molar volume. In this case the acidifying is then concurrently
realized by the chemical reaction:
CO.sub.2+H.sub.2O..fwdarw.H.sub.2CO.sub.3H.sup.++H.sup.+CO.sub.3.sup.-
[0063] More particularly, the infusing with the gaseous mixture of
11% carbon dioxide preferably transpires until both (1) the ballast
water is hypercapnic to 20 ppm carbon dioxide, and (2) the same
ballast water is acidic to pH 7. As before, the infusing and,
consequent to the infusing, the acidifying preferably transpires by
bubbling the gaseous mixture through the ballast water. Likewise
that the infusing (of CO.sub.2) preferably transpires the same in
the basis, and in the extended, methods, so also does the depleting
(of O.sub.2) preferably transpire the same even when the
consequence of the depleting is measured in the acidification, or
the lowering of the pH of the ballast water, instead of, or in
addition to, the inducing of hypercapnic and/or hypoxia conditions.
Further likewise, the depleting (of CO.sub.2) and/or the depleting
(of O.sub.2) preferably transpires by the same bubbling process,
when the consequence of the depleting is measured in the
acidification, or the lowering of the pH of the ballast water,
instead of, or in addition to, the inducing of hypocapnic and/or
hypoxia conditions.
[0064] In simple terms, the process steps of the present invention
are consistent, and synergistic. Everything works together, in
concert and to the same end: the killing of aquatic nuisance
species in ship's ballast water. Each one of the organism's three
killing `guns` i.e. hypercapnia, hypoxia, and low pH have their own
unique capability to `kill` organisms, but it does not appear that
any art prior addresses that synergistic effects of all three
elements or `guns` simultaneously.
[0065] The permeated gaseous mixture is preferably the output of a
marine inert gas generator. This gaseous mixture that is output
from a marine inert gas generator consists essentially of nitrogen
in the range from 87% to 84% mole percent, carbon dioxide in the
range from 14% to 11% mole percent, and oxygen in the range from 2%
to 4% mole percent.
[0066] Regardless of the particular ratios of the gaseous
components of the gaseous mixture, the permeation is most
preferably continued until the ship's ballast water is hypoxic to
.ltoreq.0.8 ppm oxygen, hypercapnic to .gtoreq.50 ppm carbon
dioxide, and acidic to pH.ltoreq.6.
* * * * *